The invention relates to a frequency hopping method used in a base station comprising baseband processing means, the method comprising formation of RF sub-bands, to which signals are transmitted and from which signals are received in a broadband form, and the signals transmitted in the method are made to hop according to a frequency hopping sequence, and the received signals being subjected to dehopping.
In cellular radio systems, the quality of a connection between a base station and subscriber terminals varies as a function of time and place. On average, the further the terminal equipments are situated from the base station, the more a signal is attenuated over the radio path. There are also other factors, such as obstructions and outside interference, affecting the quality of the signal at the reception.
GSM systems can employ a slow frequency hopping (SFH) method. In the frequency hopping a carrier wave is made to hop over the entire frequency band according to a predetermined sequence. The sequence used in the hopping can be, for example, a pseudo-random sequence. The primary advantage of slow frequency hopping is frequency diversity. When the data to be transmitted is provided with redundancy by means of encoding, the original data of the signal can be discovered even if the detected data signal contains errors. In signal transmission a data block is spread into several different bursts. By means of the slow frequency hopping it is possible to ensure that the information is transmitted on several frequencies so that the transmission capacity is improved. Due to frequency hopping the quality of the transmission can be improved particularly in situations where a terminal equipment moves very slowly or does not move at all, as it often happens when calls are made with mobile phones, for example.
On the other hand, frequency hopping is also useful when interference caused by a radio connection is scattered to several frequencies, in which case momentary interference on a particular frequency remains small. Similarly, strong interference received on a particular frequency causes errors only in a part of the data block. In such a case the original data can be detected without errors from the signal.
In several systems some of the channels used by the base station are frequency hopping channels, whereas some channels use fixed frequencies. This is necessary since some channels, such as signalling channels, must be transmitted on a particular frequency in order that they can be located by the terminal equipments. This is one of the reasons why different traffic channels of a base station can have rather different interference levels.
Prior art radio systems employ base stations comprising broadband transceiver units, which enable reduction of the base station size and the manufacturing costs. In some systems insufficiently developed technology has made it impossible to build a transceiver whose bandwidth would cover the entire frequency band allocated to the system.
The problems appearing in the implementation of broadband transceiver units mainly occur in elements that carry out D/A and AID conversions and in linear power amplifier parts. Therefore it is not possible to optimally utilize a frequency band in the radio systems.
The aforementioned effects of the problems can be reduced by providing a base station with several broadband transceiver units, each of which covers a particular RF sub-band, so that the entire frequency band will be covered. Broadband transceiver units of prior art base stations employ baseband parts which are fixedly connected. In the situation described above, a signal which has propagated via a particular baseband part is connected to a specific transceiver unit. However, the prior art method restricts the frequency hopping to a particular RF sub-band, wherefore the use of the frequency hopping is not as efficient as it could be.
The purpose of the invention is to provide a method and equipment implementing the method, which solve the problems described above. This is achieved with a method of the type described in the introduction, which is characterized in that when the base station comprises channelling means, the RF sub-band and the channelling means to which a baseband signal formed by the baseband processing means is connected are selected according to the frequency hopping sequence in the transmission direction of the base station, the baseband signals connected to the channelling means are placed on an intermediate band according to the frequency hopping sequence in the transmission direction, the RF sub-band and the channelling means to which each baseband processing means is connected are selected according to the frequency hopping sequence in the direction of reception, the signals received by the channelling means, which are on the intermediate band, are placed on baseband outputs of the channelling means according to the frequency hopping sequence in the direction of reception.
The invention also relates to a base station comprising at the transmitter end a number of baseband processing means and broadband transmitter units, which form RF sub-bands and transmit frequency hopping signals according to a frequency hopping sequence to the RF sub-bands they have formed.
The base station according to the invention is characterized in that the base station comprises at the transmitter end a switching means and channelling means, which generate signals on an intermediate band and each of which is connected to a transmitter unit forming a particular RF sub-band, the switching means selects, according to the frequency hopping sequence, the channelling means to which a baseband signal formed by the baseband processing means is connected, the channelling means places the received baseband signals on an intermediate band according to the frequency hopping sequence.
The invention further relates to a base station comprising at the receiver end a number of baseband processing means and broadband receiver units, which form RF sub-bands and receive frequency hopping signals according to a frequency hopping sequence from the RF sub-bands they have formed.
The base station according to the invention is characterized in that the base station comprises at the receiver end a switching means and channelling means, which receive baseband signals from an intermediate band and each of which is connected to a receiver unit forming a particular RF sub-band, the switching means selects, according to the frequency hopping sequence, the channelling means whose baseband output provides the baseband signal which is connected to the baseband processing means, the channelling means places the baseband signals to its baseband outputs according to the frequency hopping sequence.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on coordinated cooperation of switching means and channelling means provided in the base station, whereby any baseband signal can be connected to any transmitter unit. Therefore the signal forming the connection can be made to hop over the entire frequency range. A switching means provided at the receiver end of the base station connects signals from several different RF sub-bands to any baseband processing unit according to the received signal. An RF sub-band has been assigned in advance to the transmitter unit of the base station, which transmits a signal to this sub-band. The RF sub-bands of different transmitter units form an actual frequency band, and the signals transmitted to this band constitute a signal forming the connection. Also, each receiver unit receives a signal from a predetermined RF sub-band, whereafter the signal forming the connection can be formed from the signals of different sub-bands.
The method and the base station according to the invention provide several advantages. The method according to the invention enables frequency hopping on the entire frequency band allocated to the base station, even in a case where the technology restricts the bandwidth of the broadband transceiver units to a narrower level than the entire frequency band allocated to the base station. Optimum frequency and interference diversity can thus be achieved.